Mining high-gas coal seams in China has the characteristics mining of deep, high storage and low permeability, and low drainage efficiency, which seriously restrict the efficient prevention and control of mine gas disasters. Based on the characteristics of low viscosity and permeability, phase change pressurization, and strong adsorption potential energy of liquid CO₂, the technology system of liquid CO₂ displacement for high-gas and low-permeability coal seam was developed, and field industrial of low-pressure (0.52.5MPa) and medium-pressure (2.515.0MPa) combined injection test was carried out. In this test, the mode of injection followed by drainage was adopted, and the gas drainage effect was investigated for 30 days. The test results show that the effective influence radius of CO₂ in this test is 20m, and the liquid seepage radius is 5 to 7m. After the injection of liquid CO₂ into coal seam, the average gas drainage concentration and drainage purity of all drainage holes were increased by 3.2 and 3.4 times, respectively, and the gas promotion effect was significant. Taking the liquid CO₂ low-medium-pressure displacement gas test area as the calculation unit, from the comprehensive benefit analysis, compared with the original drainage mode, the liquid CO₂-combined pressure injection process can save 34.7 of the engineering cost and shorten the gas drainage standard time by 45.9. Therefore, the application of this technology has important technical support and reference significance for the efficient management of gas in the same type of mine.

Implementing a sealing measure on both ends of the mine tunnel fire is an important approach for fire extinguishing. In order to explore the effect of different sealing velocities on the temperature distribution of mine tunnel fire during dynamic sealing, a series of full-scale mine tunnel fire models were built using Pyrosim, and Fire Dynamics Simulator (FDS) was carried out to investigate the smoke temperature beneath the tunnel ceiling in symmetrical sealing on both ends. The results show the sealing method led to a substantial increasement of the mine tunnel ceiling temperature when the HRR was relatively small (2 MW). And with the acceleration of the sealing velocity, the time to reach the maximum temperature was earlier. However, the HRR was greater than 6 MW, the sealing velocities have less impact on the maximum ceiling temperature. Due to dynamic sealing of the mine tunnel fire with natural ventilation conditions, the ceiling temperature expressed an exponential decay along the longitudinal direction. Meanwhile, with the increase of the HRR, fire extinguishing time was generally advanced. When the sealing velocity was relatively slow, the maximum ceiling temperature exhibited a hysteresis, and the temperature of outside the sealing wall declined slowly. The research has great significance for mine tunnel fire control and rescue.

Coal mine gas disasters have severely restricted production safety. Improving gas extraction efficiency can effectively reduce disasters. Scholars have confirmed that CO₂ successfully displaces coal seam CH₄. This study conducted displacement and in situ experiments and compared gas drainage under different injection pressures. The displacement experiments indicated that CH₄ production rates increased under increased pressures while the displacement ratios decreased. The pressure had a positive effect on sweep efficiency. The in situ experiment showed that CH₄ and CO₂ concentration trends in the inspection hole remained consistent. Through observing the data of the original and inspection holes, the average gas drainage concentration during low- and medium-pressure injections increased by 0.61 times and 1.17 times, respectively. The low-pressure average gas drainage scalar was increased by 1.08 times. During the medium-pressure injection, the average gas drainage purity increased by 1.94 times. The diffusion ranges of CO₂ under low- and medium-pressure injections were 20–25 m and 25–30 m, respectively. The sweep efficiency of medium-pressure injection was 26% better than that of the low-pressure injection, with average pressures of 2.8 MPa and 1.4 MPa, respectively, for sweep efficiency. This study proposes an effective method for improving coal mine gas drainage efficiency.

Over the past few decades, the spontaneous combustion of large-scale coal stockpile is frequent due to natural airflow contacted the surface and entered in the voids of coal stockpile, coal is oxidized and accumulated the heat, and then coal spontaneous combustion occurred, which seriously caused the waste of natural resources and environmental pollution. In this study, based on the principle of heat transfer by heat pipe (HP), an experiment is conducted to study the effect of heat transfer by HP, such as the temperature difference and heat transfer ratio, heat transfer radius, cumulative heat transfer volume, in a coal stockpile as its heating temperature increased from 100°C to 150°C under the different lab conditions. The results indicated that the average temperature drop scale in the coal stockpile by HP was 46.3%, 10.8%, and 32.8% that under the lab conditions, respectively. A comparison study revealed that as the inserted angle of HP in the coal stockpile is 60º, the heat transfer effect of HP is significantly affected by outside ambient, especially sensitive to airflow. For instance, as the HP inserted scale is 1:4, outside air velocity is 2.0 m/s, the maximum heat transfer radius in the coal stockpile is 49.2 cm, the overall heat transfer effect enhanced by 79% and 93% that with the heating temperature in the coal stockpile is 100°C and 150°C, respectively. Therefore, it can be concluded that the utilization of HP is a reasonable method to remove the accumulated heat in the coal stockpile, as well as the suitable arrangement is also significantly important before this technique is conducted. This study provided a new technical approach and theoretical basis for the prevention and control before the large-scale stockpile has the risk of spontaneous combustion.